As computers become more powerful, the interfaces that typical programs present to users have become increasingly graphical. In order to let users select and manipulate objects in these graphical worlds, or to allow users to shift the viewpoint presented on-screen, many non-keyboard computer input devices have been created. Two of the most popular of these devices are the computer mouse and the computer joystick. A typical mouse and its method of operation are described in U.S. Pat. No. Re. 32,632 incorporated herein by this reference. The mouse is an example of a displacement or spacial mapping type of input device. Another example is the trackball. The mouse has become the most popular controller for computer programs other than video games. For video games, the joystick is the most popular device. The reason for these separate domains is simple. Identifying particular screen locations (or areas) is the primary non-keyboard input required for most programs that are not video games, e.g. word processors. For quickly and precisely indicating a position on a 2D surface, the mouse is a superior device to any form of joystick, but the mouse is inferior for indicating a constant direction of motion. The joystick, on the other hand, is poorer for indicating specific positions, but it can indicate a desired direction of movement indefinitely. The mouse's superiority for position selection is conferred by the fact that the mouse's working surface is a spatial map of what's on the monitor, so the user can almost instantly indicate any point. The mouse's problem with continuous indication of direction is the same, it is spatially mapped. Thus, in order to move an on-screen object continuously in a selected direction, one must repeatedly readjust the relationship between the mouse's position on its working surface (e.g. a mouse pad) and the on-screen object. That is, one must lift the mouse up, decoupling it from cursor movement and put it down in a different place. Continuous movement in one direction requires that this maneuver be performed repeatedly.
The joystick's superiority for direction indication derives from its basic design. When the user puts pressure on the joystick sensors, that indicates that motion is desired in the given direction. The motion will be sustained until the user releases pressure on the sensors. However, in order to indicate a particular point, the joystick user must push precisely in the direction of the desired point. Then the user must release the joystick at the exact instant that the on-screen object, such as a cursor, is in the desired position. This procedure is more difficult and less precise than mouse usage because humans are better at working with spatial mappings than with acceleration mappings.